Spindle motor with magnetic seal

ABSTRACT

The present invention relates to a spindle motor with a magnetic seal. A method and an apparatus are described for sealing spindle motors, preferably those used for disk storage units.

[0001] The invention relates to a spindle motor with magnetic sealaccording to the introductory parts of Claims 1 and 5.

[0002] Small-sized spindle motors of this type are used especially asmotors for disk storage units. These are usually collectorless DCmotors, which have the problem that the bearings need to be extremelywell sealed so that no oil from the bearings can penetrate into theclean air space around the motor, where the disks are located.

[0003] It is known to provide suitable sealing arrangements at the endopenings between the armature and the fixed stator. In one such knownarrangement, the seal may take the form of a magnetic seal essentiallycomprising two metal disks positioned a certain distance apart, betweenwhich a permanently magnetic disk is trapped.

[0004] A gap is thus formed on the radially inner side (i.e. towards thefixed shaft). This gap is filled with a ferromagnetic fluid, which iskept in place by the permanent magnet trapped between the two metaldisks. Such a magnetic seal arrangement is known, for sealing either theupper end of the motor or the lower end of the motor, and in many casesboth.

[0005] It is likewise known to use a cap, usually made of metallicmaterial, as the outermost element of this magnetic seal. The functionof this cap is to seal and protect the magnetic seal from the exterior.A known way of bringing this about is to bond such a cap into the openrecess in the hub of the armature to seal it in place. This ensures thatthe cap, the ultimate and outermost element of the magnetic seal, willprevent foreign bodies from the exterior from getting into the magneticseal.

[0006] Hitherto, it has moreover been known to form this cap as adisk-shaped body with a uniformly profiled rim all round. This, however,has the drawback that it is necessary to bond both the magnetic sealand, in a separate operation, the cap, thus increasing the labour cost.Moreover it takes up an excessive amount of space, as two sealarrangements (two beads of adhesive) have to be put in place, oneaxially superimposed above the other. This increases the overall heightof the motor.

[0007] Therefore the fundamental problem which the invention seeks tosolve is to develop a way of sealing the magnetic seal for a spindlemotor of the kind stated in the introduction which both reduces theheight required for its installation and simplifies the sealingoperation so that the labour cost is reduced.

[0008] For the solution of the stated problem, the invention ischaracterized by the technical teaching of Claims 1 and 5.

[0009] The essential feature of the invention is that both the cap andthe magnetic seal are bonded to the open seat in the hub with a singlebead of adhesive.

[0010] This makes it possible for the first time to greatly reduce theoverall height of a spindle motor of this type by virtue of the factthat only one adhesive bead is required in the axial assembly, and nottwo beads needing to be placed one above the other and spaced apart.

[0011] It is achieved by shaping the cap so that it is capable of beingbonded by the adhesive bead to the inner open seat in the hub and yetforms openings through which adhesive is able to flow past the outeredge of the cap to the magnetic seal beneath. Thus the radially outerrim of the cap and the radially outer rim of the underlying magneticseal are bonded in place with a single bead of adhesive.

[0012] This is achieved by forming suitable gaps or openings at thecap's outer edge, instead of forming it as an unbroken rim.

[0013] In a first embodiment, such gaps or openings are formed by makingthe rim of the cap smaller than the diameter of the inner seat, so thata gap is formed between this smaller rim and the internal diameter ofthe seat in the hub, and the adhesive bead is able to flow through thesaid gap, past the cap, to the magnetic seal beneath, and bond the rimof the upper disk of the magnetic seal to its seat in the hub.

[0014] Furthermore this is achieved by providing lobes which projectradially outwards beyond the said rim and whose outer peripherycorresponds to the internal diameter of the seat in the hub.

[0015] Preferably, a plurality of radial lobes are uniformly distributedaround the circumference of the cap and are integrally joined thereto.The lobes then centre the cap in the central seat in the hub.

[0016] A uniform bonding gap is then obtained, as all the gaps betweenthe inner rim of the cap and the inner circumferential face of the seatare uniformly centred, so that an even distribution of adhesive isassured.

[0017] In a preferred configuration of the present invention, instead ofradially outwards pointing lobes uniformly distributed around itscircumference, the cap is provided with a uniform, basically closed,peripheral rim, and, in the region of that rim, recesses, openings orslots are provided through which the adhesive is likewise able to flowto the magnetic disk beneath, to bond the edge thereof to the seat'sinner wall.

[0018] Because the adhesive essentially runs into the gaps between thecap's outer rim and the surface of the magnetic disk beneath, theapplication of adhesive in the end region of this spindle motor is verythin, and this greatly reduces the overall height of the motor. The factthat adhesive is also deposited on the lobes, making a joint with theadjoining wall of the seat in the hub, is insignificant, because theadhesive which is deposited on the lobes essentially runs off the lobesto left and right and into the gaps formed between the cap and themagnetic disk beneath.

[0019] The subject-matter of the present invention is disclosed not onlyby the subject-matter of the individual claims, but also by theindividual claims taken in combination.

[0020] All details and features disclosed in the documents (includingthe Abstract), and in particular the physical embodiment illustrated inthe drawings, are claimed as essential to the invention, in so far as,taken separately or in combination, they are novel with respect to thestate of the art.

[0021] The invention will now be described in detail with reference todrawings illustrating several ways in which the invention may be carriedout. Further features essential to the invention and advantages of theinvention will become apparent from the drawings and from thedescription thereof.

[0022] In the drawings:

[0023]FIG. 1 is a schematic section through a spindle motor according tothe invention

[0024]FIG. 2 is a larger-scale section view of the upper region of thespindle motor

[0025]FIG. 3 is a schematic section through a spindle motor according tothe invention with an upper seal unit

[0026]FIG. 4 is a schematic section through a spindle motor according tothe invention with a lower seal unit

[0027]FIG. 5 is a schematic section through a spindle motor according tothe invention with both upper and lower seal units

[0028]FIG. 6 is a top view of the cap, the spindle motor being viewed inthe direction of Arrow III in FIG. 1

[0029]FIG. 7 is a top view of the spindle motor with cap.

[0030]FIG. 1 is a general view of a spindle motor with a fixed baseplate1 which accommodates a stator iron core 2 with its winding 3. The saidparts 1-3, in conjunction with a fixed shaft 5 about which the hub 4 ofan armature rotates, form the stator. A lower bearing 6 and an upperbearing 7 serve as rotational bearings. These bearings 6, 7 are sealedoff from the outer atmosphere by [lower and upper] end shields 9, 10respectively, to prevent oil particles from escaping into theatmosphere.

[0031] The significant point is that a seal unit 11 equipped with amagnetic seal is arranged in the upper region of this spindle motor.

[0032] However, the invention is not limited to the provision of anupper seal unit 11. This seal unit 11 can also be provided in the lowerregion of the spindle motor, i.e. below the lower bearing 6. Or twomagnetic seal arrangements may be provided, namely an upper seal unit 11and a lower seal unit, as shown in FIG. 5.

[0033] Another possibility, shown in FIG. 4, is a third embodiment inwhich only a lower seal unit is provided, and the upper seal unit isomitted.

[0034] The upper seal unit 11 essentially consists of a magnetic seal12. This comprises two metal disks 13 which are spaced apart, formingbetween them a gap which is occupied by a permanent magnet disk 14. Inthe radially inwards direction the two metal disks 13 form a magneticslot in conjunction with the permanent magnet disk 14, and the region ofthis slot 15 is filled with a ferromagnetic fluid 16 which is kept inthis slot 15 by the action of magnetism. This fluid is drawn onto theouter circumferential face of a seal sleeve 17 (made of magneticallyconductive steel), so forming a seal. The seal sleeve is press-fitted ona central screwed seat 18 which, in turn, forms part of the fixed shaft5.

[0035] The inner ring 19 of the upper bearing 7 is press-fitted orbonded at its inner circumferential face onto the outer circumferentialface of a knurled sleeve 20 fixed to the shaft 5. Above the upperbearing 7 is the end shield 10 previously mentioned, which establishes agap (accommodation space 21) with respect to the lower metal disk 13 ofthe magnetic seal 12. This space (accommodation space 21) serves toaccommodate ferromagnetic fluid 16 escaping from the meniscus of fluid16 formed on the outer circumferential face of the sleeve 17.

[0036] The same applies to the upper accommodation space 23 formedbetween the upper metal disk 13 and the cap 22 according to theinvention.

[0037] The significant point is that the cap 22 has been bonded into theinner seat, i.e. to the wall 27 of the hub 4, with a single bead 26 ofadhesive, and the magnetic seal 12 has been bonded in placesimultaneously by this same adhesive bead 26.

[0038] First, as FIG. 3 shows, the cap 22 essentially consists of a bodyin the shape of a flat disk but with a joggle 24 in its outer region.The purpose of this joggle is to establish the accommodation space 23for the overspill of ferromagnetic fluid 16.

[0039] The significant point is that the cap 22 has radially outwardsdirected lobes 25 uniformly distributed around its periphery. The outerdiameter of these lobes (edge 30) is chosen to fit snugly into the innerdiameter 32 of the seat in the hub 4. That is to say, the edges 30 ofthe lobes 25 are flush with the inner wall 27 of the seat.

[0040] Set back from the lobes 25 there is a rim 28 with a smallerdiameter.

[0041]FIG. 3 shows a schematic section through a spindle motor accordingto the invention with an upper seal unit. The form of the armature isslightly modified in relation to that shown in FIG. 1.

[0042]FIG. 4 shows a schematic section through a spindle motor accordingto the invention with a lower seal unit. The form of the armature isslightly modified in relation to that shown in FIG. 1.

[0043]FIG. 5 shows a schematic section through a spindle motor accordingto the invention with upper and lower seal units. The form of thearmature is slightly modified in relation to that shown in FIG. 1.

[0044]FIG. 6 shows, in a top view of the end seal arrangement, that agap 31 is thereby formed between the inner rim 28 of the cap 22 and theouter edge 30 of the projecting lobes 25. Into this gap, which is openat the top, and also onto the lobes 25, a bead 26 of adhesive is placed,some of which lands on the lobes 25, but which also runs into the gap 31and, as FIG. 2 shows (on the right-hand side of the drawing), isdeposited on the surface of the upper metal disk 13 of the magnetic seal12. In this way, the rim of the magnetic seal 12 is bonded to the innerwall 27 of the seat, and the cap is bonded to the same inner wall 27with the same bead of adhesive through the bonding of the lobes 25.

[0045] Thus the adhesive bead is laid on the surface 29 of the uppermetal disk 13 of the magnetic seal 12, forming a bonded joint to theinner wall 27.

[0046] The right-hand side of FIG. 2 shows that the rim 28 ends at ashort distance from the wall 27, that is to say, the gap 31 previouslymentioned in [the context of] FIG. 3 is formed, into which the adhesivebead 26 is able to flow down from above.

[0047] Of course, bonding of the cap to the wall 27 by the bead 26 doesnot only take place at the lobes. Because the adhesive bead alsooverlaps the rim 28, the cap is bonded all round its periphery to thewall 27, and at the same time the magnetic seal 12 is also bonded tothis wall 27.

[0048] As well as the fixing effect of the bonding, an excellent sealingeffect is simultaneously obtained, as the adhesive bead runs completelyround. In other words, the bead is closed all round, so that this outerrim is bonded and sealed over its entire periphery.

[0049] Drawing Legend

[0050]1. Baseplate

[0051]2. Stator iron core

[0052]3. Winding

[0053]4. Hub (armature)

[0054]5. Shaft

[0055]6. Lower bearing

[0056]7. Upper bearing

[0057]8. Outer ring

[0058]9. End shield, lower

[0059]10. End shield, upper

[0060]11. Seal unit

[0061]12. Magnetic seal

[0062]13. Metal disk

[0063]14. Permanent magnet disk

[0064]15. Slot

[0065]16. Ferromagnetic fluid?

[0066]17. Seal sleeve

[0067]18. Screwed seat

[0068]19. Inner ring of bearing

[0069]20. Knurled sleeve

[0070]21. Accommodation space

[0071]22. Cap

[0072]23. Accommodation space

[0073]24. Joggle

[0074]25. Lobe

[0075]26. Adhesive bead

[0076]27. Wall (hub)

[0077]28. Rim

[0078]29. Surface

[0079]30. Edge (lobe)

[0080]31. Gap

[0081]32. Inner diameter (hub)

1. Method for sealing a spindle motor with a magnetic seal betweenstator and armature, comprising metal disks spaced apart and a magneticdisk arranged between them, and ferromagnetic fluid arranged to providea seal towards the armature, and also an outer closure element in theform of a cap for protection against penetration of foreign bodies tothe exterior, particularly for use in disk storage units, characterizedin that both the cap (22) and the magnetic seal (12) are bonded to theopen seat in the hub (4) with a single adhesive bead (26).
 2. Methodaccording to claim 1, characterized in that the adhesive bead (26) forboth cap (22) and magnetic seal (12) is applied in a single operation.3. Method according to claim 1 or claim 2, characterized in that afterthe adhesive bead has been applied the adhesive distributes itself moreor less uniformly around the periphery of the cap (22) and magnetic seal(12), and the greater part of it is drawn into the gaps throughcapillary action, leaving only a very thin layer of adhesive on the endface of the spindle motor.
 4. Method according to claim 1 or claim 2,characterized in that the overall height of the spindle motor measuredin its axial extension is greatly reduced by the application of only onebead (26) of adhesive to fix the magnetic seal (12) and cap (22). 5.Spindle motor with a magnetic seal between stator and armature,comprising metal disks spaced apart and a magnetic disk arranged betweenthem, and ferromagnetic fluid arranged to provide a seal towards thearmature, and also an outer closure element in the form of a cap forprotection against penetration of foreign bodies to the exterior,particularly for use in disk storage units, characterized in that themagnetic seal (12) and the cap (22) are bonded in the hub (4) withouthaving to be spaced apart from each other.
 6. Spindle motor according toclaim 5, characterized in that the radially outer rim (28) of the cap(22) is formed so as to leave a peripheral gap between it and the wall(27) of the hub (4).
 7. Spindle motor according to claim 5,characterized in that the radially outer rim (28) of the cap (22) isformed so that it has openings leading to the magnetic seal beneath. 8.Spindle motor according to claim 5, characterized in that the radiallyouter rim (28) of the cap (22) is formed so that it has radiallyoutwards pointing lobes.
 9. Spindle motor according to claim 5,characterized in that the radially outer rim (28) of the cap (22) isbasically closed, but approximately radially encircling [sic] recesses,openings or slots are disposed in the region of that rim.
 10. Spindlemotor according to any one of claims 5 to 9, characterized in that aseal unit (11) is arranged in the upper region of the spindle motor. 11.Spindle motor according to any one of claims 5 to 9, characterized inthat a seal unit (11) is arranged in the lower region of the spindlemotor.
 12. Spindle motor according to any one of claims 5 to 9,characterized in that seal units (11) are arranged in both upper andlower regions of the spindle motor.
 13. Spindle motor according to anyone of claims 5 to 12, characterized in that the magnetic seal (12)consists of two metal disks (13) which are spaced apart, forming betweenthem a gap which is occupied by a permanent magnet disk (14). 14.Spindle motor according to any one of claims 5 to 13, characterized inthat in the radially inwards direction the two metal disks (13) form amagnetic slot in conjunction with the permanent magnet disk (14), and aferromagnetic fluid 16 is contained in the region of this slot (15) andis kept there by the action of magnetism.
 15. Spindle motor according toany one of claims 5 to 14, characterized in that the ferromagnetic fluidis drawn onto the outer circumferential face of a seal sleeve (17) whichis made of magnetically conductive steel, so forming a seal.
 16. Spindlemotor according to any one of claims 5 to 15, characterized in that theseal sleeve is press-fitted on a central screwed seat (18) which, inturn, forms part of the fixed shaft (5).
 17. Spindle motor according toany one of claims 5 to 16, characterized in that an accommodation space(21, 23) serves to accommodate ferromagnetic fluid (16) escaping fromthe meniscus of fluid (16) formed on the outer circumferential face ofthe sleeve (17).
 18. Spindle motor according to any one of claims 5 to17, characterized in that the cap (22) essentially consists of a flatdisk-shaped body which has a joggle (24) in its outer region, to formthe accommodation space (23).